The present disclosure relates generally to the etching of native oxides on a wafer, and more particularly to plasma-based etching of native oxides and polysilicon with a high selectivity on a wafer.
Plasma-based etching can be an important processing step in the fabrication of semiconductor devices and integrated circuits. However, the presence of a native oxide layer on the surfaces of many materials, including semiconductor substrates containing silicon and metals, can adversely affect the patterning of such materials. This can be an important part in the fabrication of semiconductor chips or memory devices. For example, a native oxide layer on polysilicon can substantially suppress and increase the non-uniformity of the etching of polysilicon. A native oxide layer may form when a silicon-containing surface is exposed to ambient conditions or oxygen.
Typically, removal of native oxides can be performed using wet processes, such as treating the native oxide with dilute hydrofluoric acid (HF). However, the use of such a wet etching process for removing native oxides may be expensive, may pose serious safety concerns, may not achieve a high selectivity over other materials, and may cause additional exposure to ambient conditions to allow native oxides to regrow prior to etching polysilicon. Wet processes may also be problematic for devices involving high-aspect-ratio features.
Typically, removal of polysilicon can be performed using wet or dry reactive-ion-etch (RIE) processes. However, a wet etching process for removing polysilicon can result in a low etch rate of polysilicon, which leads to a low throughput. Furthermore, a wet etching process for removal of polysilicon may not achieve as high of selectivity over other materials as dry etching processes.
A dry RIE process can result in greater cost due at least in part to complicated hardware for controlling ion direction and energy using an external bias. In addition, the use of a dry RIE process can damage surrounding structures due to exposure to ion and photon fluxes. The surrounding structures can be sidewalls made of, for example, exposed nitrides and/or oxides. Such surrounding structures can include silicon nitride (Si3N4), titanium nitride (TiN), and silicon oxide (SiO2) including thermal oxide.